A transistor, made of a solid piece of semiconductor material, is a semiconductor device used to amplify and switch electronic signals. It has at least three terminals for connection to an external circuit. A voltage or current applied to one pair of transistor's terminals changes the current flowing through another pair of terminals. The transistor amplifies the signal since the controlled power can be much more than the controlling power. The transistor is a fundamental building block of...

A pivoted catch designed to fall into a notch on a ratchet wheel so as to allow movement in only one direction (e.g. on a windlass or in a clock mechanism), or alternatively to move the wheel in one direction.